Nah, nevermind. But x86-32 software runs fine on x86-64 OS.

So, i buy ram (3000 HUF only) and try Windows7 on his PC.

The Celeron is the slowest thing there, I would never use a Celeron, even if it is only 10% load, I idle at around 1% using a 2.66 GHz Core 2 Duo.

The thing about a Celeron is it's designed for a low-end crap computer, something not worth using.

If I was to use any of the latest pre-RTM builds of Windows 7 available here (Build 7264 for 32-bit x86 systems, and Build 7600.16384 for x64, that is, x86 64-bit systems) in place of the actual RTM version, I would certainly convert it to Service Pack 1 by installing Service Pack 1 over the current build, even if it requires certain modifications to some files (maxtorix has done this before, and in problematic economic situations such as kopp's, and also cases of merely testing and collecting the software itself, I support such procedures, but not when the user would otherwise be able to aquire it legally).

Also, as for copies of Windows not being legal, I don't see how that would slow down your system. It sounds to me more like the software being used on it that is bloating down your system, not anything relating to the legality and origin of your Windows Setup files.

However, at this point, if you can't easily aquire a legal copy of Windows 7, then I might just go with Windows 8, reinstalling to the latest builds being released once they become available, since not only would you be aquiring it by the same means as Windows 7 in this case (that is, if you decided to use either version of Windows), but it's superior to Windows 7 anyway, especially in terms of functionality and performance (performance is especially important in this case, since you also say that your system is operating slowly).

If it was me, I would say that you're much better off with Windows 8 at this point, especially considering that this seems to be your only way of obtaining copies of the latest versions of Windows, however, it's your choice which version of Windows you want to choose for your family's system.

I forgot the slmgr rearm on Windows 7 :
Instructions :
1- Install Windows 7 (whatever edition/architecture you want)
2- Don't enter a product key
3- When there is 1 day remaining for activation, execute "slmgr -rearm" on Command Prompt. (Be sure to execute the command prompt in Administrator mode)
4- Do it three times.
5- After 120 days (4 months), you will have to reinstall Windows.
This also works for Vista.

What does that do? Does that disable activation, or does it have to do with something else?

Anyway, that being said, using the latest available Release Candidate or pre-RTM version of Windows in place of the RTM "Gold" version, and converting it to a Service Pack release, is probably the best way to achieve RTM functionailty, that is, if you don't have proper access to the official RTM release, and no practical way to aquire an actual copy of it.

In fairness, it's a "Conroe" celeron, so it is using the same architecture as the original Core 2 Duos.

Only having 1GB is the biggest factor on that PC, and RAM is pretty cheap these days, so it'll be by far the most cost-effective upgrade for him.

You could try reinstalling the whole OS. Or you could defragment the hard drive, do disk cleanup. Or use AVG PC Tuneup to clean up registery errors, junk files etc.

I suggest you to upgrade ram...
For more faster change you processor...